Nanoplate-nanotube composites, methods for production thereof and products obtained therefrom

ABSTRACT

Compositions and methods of producing discrete nanotubes and nanoplates and a method for their production. The discrete nanotube/nanoplate compositions are useful in fabricated articles to provide superior mechanical and electrical performance. They are also useful as catalysts and catalyst supports for chemical reactions.

This application is a continuation-in-part of U.S. patent applicationSer. No. 14/128,350 which will issue as U.S. Pat. No. 9,475,921 andwhich claims priority to PCT/US2012/043533 filed Jun. 21, 2012 and U.S.Provisional Patent Application Ser. No. 61/500,562, entitled“GRAPHENE-CARBON NANOTUBE COMPOSITES, METHODS FOR PRODUCTION THEREOF ANDPRODUCTS OBTAINED THEREFROM,” filed on Jun. 23, 2011, U.S. the entirecontents of which are hereby incorporated by reference. This applicationis also related to U.S. application Ser. No. 13/529,784 filed Jun. 21,2012.

FIELD OF THE INVENTION

The present invention is directed to compositions and methods ofproducing nanoplates and nanotubes.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention relates to a composition of nanoplates andnanotubes wherein at least a portion of the nanoplates have at least onenanotube interspersed between two nanoplates. In particular, isdescribed the exfoliation and dispersion of carbon nanotubes andgraphene structures resulting in high aspect ratio, surface-modifiedcarbon nanotube/graphene compositions that are readily dispersed invarious media. Graphene structures here is meant to include graphene andoxygenated graphene structures. The carbon nanotubes here is meant toinclude carbon nanotubes and oxidized carbon nanotubes. The oxygenatedstructures of carbon nanotubes or graphene include, but are not limitedto, carboxylic acid, amide, glycidyl and hydroxyl groups attached to thecarbon surface.

These nanoplate-nanotube mixtures can be further modified by surfaceactive or modifying agents. This invention also relates tonanoplate-nanotube composites with materials such as elastomers,thermosets, thermoplastics, ceramics and electroactive or photoactivematerials. The graphene-carbon nanotube compositions are also useful ascatalysts for chemical reactions. Also, the present invention pertainsto methods for production of such composites in high yield.

Carbon nanotubes in their solid state are currently produced asagglomerated nanotube bundles in a mixture of chiral or non-chiralforms. Various methods have been developed to debundle or disentanglecarbon nanotubes in solution. For example, carbon nanotubes may beshortened extensively by aggressive oxidative means and then dispersedas individual nanotubes in dilute solution. These tubes have low aspectratios not suitable for high strength composite materials. Carbonnanotubes may also be dispersed in very dilute solution as individualsby sonication in the presence of a surfactant. Illustrative surfactantsused for dispersing carbon nanotubes in solution include, for example,sodium dodecyl sulfate and PLURONICS. In some instances, solutions ofindividualized carbon nanotubes may be prepared from polymer-wrappedcarbon nanotubes. Individualized single-wall carbon nanotube solutionshave also been prepared in very dilute solutions using polysaccharides,polypeptides, water-soluble polymers, nucleic acids, DNA,polynucleotides, polyimides, and polyvinylpyrrolidone. The dilutionranges are often in the mg/liter ranges and not suitable for commercialusage.

If graphene is exfoliated, i.e., with the individual plates separatedrather than stacked, in medium such as water, the thermodynamic energiesdue to incompatibility and the very high surface area of the grapheneresults in the plates recombining, and the plates become very difficultto separate into individual plates. Likewise, if graphene plates are tobe oxidized, if the plates are bundled, then only the edges of thegraphene are readily accessible for reaction.

In the present invention, discrete tubes ranging in diameter from ananometer to 100 nanometers can be inserted between inorganic plates. Inparticular, carbon nanotubes can be inserted between graphene platesthus restricting their agglomeration and facilitating exfoliation in abroad range of materials including liquids and solids. Furthermore, asthe plates are now separated, reactions can be entertained at thesurface of the graphene plates to give, for example, oxygenated graphenestructures. The diameter of the tubes can be used to control the interplate distance. Selecting tubes of different diameters can lead tocontrolled transport of molecules or ions between the plates.

In view of the foregoing, nanoplate-discrete nanotube compositions andmethods for obtaining them are of considerable interest in the art. Anumber of uses for discrete nanotube/single inorganic plates,particularly carbon nanotube/graphene compositions, are proposedincluding, for example, energy storage devices (e.g., ultracapacitors,supercapacitors and batteries), field emitters, conductive films,conductive wires, photoactive materials, drug delivery and membranefilters. Use of discrete carbon nanotube/graphene compositions as areinforcing agent in material composites is another area which ispredicted to have significant utility. Materials include, for example,polymers, ceramics, rubbers, cements. Applications include tires,adhesives, and engineered structures such as windblades, aircraft andthe like.

One embodiment of this invention includes a composition comprisinginorganic plates with individual plate thickness less than 10nanometers, termed nanoplates, interspersed with at least a portion ofdiscrete nanotubes of diameter ranging from about 1 nanometer to 150nanometers and aspect ratio about 10 to 500. Preferably the inorganicplates are graphene and the discrete nanotubes are carbon nanotubes. Therange of weight ratio of inorganic plates to nanotubes is about 1:100 to100:1. The mixture of nanoplates and nanotubes may further comprise apolymer selected from the group consisting of thermoplastics, thermosetsand elastomers and/or inorganic materials selected from the groupconsisting of ceramics, clays, silicates, metal complexes and salts.

A further embodiment of this invention includes a mixture of nanoplatesand nanotubes which may further comprise at least one electroactivematerial, which may be useful, for example, in an energy storage deviceor photovoltaic.

A yet further embodiment of this invention is a composition ofnanoplates and nanotubes further comprising at least one transitionmetal complex or active catalyst species. An active catalyst can beionically, or covalently attached to the discrete nanotubes, orinorganic plates or combinations thereof. The chemical reactions caninvolve contact of the composition with, for example, but not limitedto, alkenes and alkynes, chemical moieties containing oxygen, chemicalmoieties containing nitrogen, chemical moieties containing halogen, andchemical moieties containing phosphorous. The composition may be in theform of a powder for gas phase reaction or in the form of a liquidmixture for solution and slurry phase reactions.

Another embodiment of this invention is a method for preparing graphenecarbon nanotube composites, said method comprising: a) suspendingnon-discrete graphene and non-discrete carbon nanotube fibers in anacidic solution for a time period; b) optionally agitating saidsuspension; c) sonically treating said suspension of graphene-carbonnanotubes to form graphene-discrete carbon nanotube fibers; and d)isolating the resultant graphene-discrete carbon nanotube compositionfrom the acid prior to further treatment using solid/liquid separations,wherein said separations comprise filtration.

Another embodiment of this invention is a method for preparing inorganicplate-carbon nanotube composites, said method comprising: a) suspendingnon-discrete carbon nanotube fibers in an acidic solution for a timeperiod, b) sonically treating said suspension of carbon nanotubes toform discrete carbon nanotube fibers, c) isolating the resultantoxidized discrete carbon nanotube composition from the acid, d) washingthe oxidized discrete carbon nanotubes with water or other liquids toremove acid, e) redispersing the discrete oxidized carbon nanotubes withinorganic plates, optionally with surfactants and sonication, f)optionally adding a polymer, g) optionally adding a transition metalcomplex, h) optionally adding an electroactive material, i) optionallyadding a ceramic, j) separating the mixture and optionally drying.

A further embodiment of this invention is the composition nanoplates andnanotubes in the form of a part of a fabricated article such as a tire,industrial rubber part or wind blade. The compositions are also usefulfor batteries, capacitors, photovoltaics catalysts and catalystsupports. Further utility is envisioned, but not limited to, membranes,conductive inks, sensors and static management and electromagneticshielding.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionsto be taken in conjunction with the accompanying figures for describingspecific embodiments of the disclosure, wherein:

FIG. 1 shows a secondary electron micrograph of graphene plates with adiscrete carbon nanotube of this invention. The magnification is200,000×.

FIG. 2 shows a secondary electron micrograph of lithium iron phosphateand magnesium hydroxide plates with a discrete carbon nanotube of thisinvention. The magnification is 5,060×.

FIG. 3 shows a secondary electron micrograph of zirconium phosphateplates with discrete carbon nanotube of this invention. Themagnification is 155,000×.

DETAILED DESCRIPTION

In the following description, certain details are set forth such asspecific quantities, sizes, etc., so as to provide a thoroughunderstanding of the present embodiments disclosed herein. However, itwill be evident to those of ordinary skill in the art that the presentdisclosure may be practiced without such specific details. In manycases, details concerning such considerations and the like have beenomitted inasmuch as such details are not necessary to obtain a completeunderstanding of the present disclosure and are within the skills ofpersons of ordinary skill in the relevant art.

While most of the terms used herein will be recognizable to those ofordinary skill in the art, it should be understood, however, that whennot explicitly defined, terms should be interpreted as adopting ameaning presently accepted by those of ordinary skill in the art. Incases where the construction of a term would render it meaningless oressentially meaningless, the definition should be taken from Webster'sDictionary, 3rd Edition, 2009. Definitions and/or interpretations shouldnot be incorporated from other patent applications, patents, orpublications, related or not, unless specifically stated in thisspecification or if the incorporation is necessary for maintainingvalidity.

Nanotubes are tubular structures that have a diameter of at least 1nanometer and up to 100 nanometers. Examples of nanotubes are single,double and multiwall carbon nanotubes or titanium dioxide nanotubes. Theaspect ratio is defined as the ratio of the tube length to the tubediameter. Nanoplates are defined as being discernible plates ofthickness less than ten nanometers.

Discrete oxidized carbon nanotubes, alternatively termed exfoliatedcarbon nanotubes, can be obtained from as-made bundled carbon nanotubesby methods such as oxidation using a combination of concentratedsulfuric and nitric acids. The bundled carbon nanotubes can be made fromany known means such as, for example, chemical vapor deposition, laserablation, and high pressure carbon monoxide synthesis. The bundledcarbon nanotubes can be present in a variety of forms including, forexample, soot, powder, fibers, and bucky paper. Furthermore, the bundledcarbon nanotubes may be of any length, diameter, or chirality. Carbonnanotubes may be metallic, semi-metallic, semi-conducting, ornon-metallic based on their chirality and number of walls. The discreteoxidized carbon nanotubes may include, for example, single-wall,double-wall carbon nanotubes, or multi-wall carbon nanotubes andcombinations thereof.

Graphene is an allotrope of carbon, whose structure is one-atom-thickplanar sheets of sp²-bonded carbon atoms that are densely packed in ahoneycomb crystal lattice. The crystalline or “flake” form of graphiteconsists of many graphene sheets stacked together. Graphene sheets stackto form graphite with an interplanar spacing of 0.335 nm. Graphene isthe basic structural element of some carbon allotropes includinggraphite, charcoal, carbon nanotubes and fullerenes. It can also beconsidered as an indefinitely large aromatic molecule, the limiting caseof the family of flat polycyclic aromatic hydrocarbons. One method forgraphene obtainment consists of mixing low concentrations of graphite ina solvent such as N-methylpyrrolidone then sonicating. Non-exfoliatedgraphite is eventually separated from graphene by centrifugation.

In one embodiment the inorganic plates are interspersed with thediscrete multiwall carbon nanotubes and both the inorganic plates, e.g.,graphene, and the discrete multiwall carbon nanotubes are oxidized. Inthis manner a negative surface charge may cause individual carbonnanotubes to repel each other and potentially prevent or further limitagglomeration and/or entanglement. This along with employing discretenanotubes may be beneficial in controlling the interplate distance sincethis distance may be primarily determined by nanotube diameter asopposed to agglomerated nanotubes as used in the prior art. Thecontrolled distance may be useful in applications wherein controlledtransport of molecules or ions between the plates is desired.

In another embodiment the composition comprises graphene inorganicplates having an individual plate thickness of less than 10 nanometersand discrete multiwall carbon nanotubes having a diameter ranging fromabout 1 nanometer to 150 nanometers, an oxidation level of from about 1weight % to about 15 weight %, and an aspect ratio ranging from about 10to 500. Depending upon the desired ion transport it may be beneficial ifthe composition does not include polymer particles in amounts such thatthe ion transport is materially affected in an undesired manner.

One of ordinary skill in the art will recognize that many of thespecific aspects of this invention illustrated utilizing a particulartype of nanotube or nanoplate may be practiced equivalently within thespirit and scope of the disclosure utilizing other types of nanotubesand nanoplates.

EXAMPLE 1

Evaluation of Discrete Carbon Nanotubes and Graphene DispersionCharacteristics in Surfactant-Stabilized Aqueous Suspensions

Graphene (Rice University) and multiwall carbon nanotubes (C-9000,C-Nano) of diameter about 13 nm and are combined in the weight ratio of1:3, respectively. A 1% w/v dispersion of the mixture is prepared in a3:1 sulfuric (96%, KMG)/nitric (70%, Honeywell) acid solution andsonicated using a sonicator bathe while maintaining a bath temperaturein the 30° C.-35° C. range for 3 hours. Following sonication, eachformulation was Büchner-filtered on a 5 μm PVDF membrane (Whatman) witha 200 mL portion of water. The samples were dried for two hours at 80°C. in a vacuum oven. An electron micrograph will show carbon nanotubesseparating graphene plates, for example shown in FIG. 1.

0.05 g of the dried graphene carbon nanotube mixture and 0.15 g ofsodium dodecyl sulfate (Sigma-Aldridge) was added to a 20 mL graduatedflask and filled o the 20 mL mark with water. The flask was sonicated ina bath for a period of 1 hour, the temperature monitored in the samefashion described above. After sonication, a 1 mL sample was dilutedwith water to final total carbon concentration of 2.5×10⁻⁵ g/mL andevaluated by UV-vis spectrophotometry (BioSpec-1601, Shimadzu).Following the measurement of the first absorbance spectrum, the samespecimen was analyzed at 5, 15, 30, 45 and 60-minute time periods at awavelength of 500 nm to evaluate the stability of the mixture in water.The decay in initial absorbance value at 500 nm after 60 minutes wasdetermined as 0.4%.

Comparison 1

Comparison 1 repeats the experimental procedure as example 1 but withgraphene only. The decay in initial absorbance value at 500 nm after 60minutes was determined as 12.1%.

Comparison 2

Comparison 2 repeats the experimental procedure as example 1 but withmultiwall carbon nanotubes only. The decay in initial absorbance valueat 500 nm after 60 minutes was determined as 0%.

The discrete carbon nanotubes of example 1 are shown by the UVspectroscopy to have provided stability to the graphene dispersions byinterspersing between the graphene plates.

EXAMPLE 2

0.039 grams of multiwall carbon nanotubes with an oxidation level of 8weight percent is added to 0.0401 grams of lithium iron phosphate and 40grams of deionized water in a glass bottle. The mixture is sonicated for13 minutes using a sonicator bath at 25 degrees centigrade, after whichno carbon nanotube particles are observed by visual inspection. 1 ml ofthe sonicated mixture is then mixed with 0.14 mls of a 0.1%weight/volume mixture of magnesium hydroxide in deionized water and thendiluted with more deionized water so that the volume was 4 ml. Thisfinal mixture was sonicated a further 15 minutes at 25 degreescentigrade. For examination by electron microscopy a drop of thissolution is then placed on a carbon tape and dried. The result is seenin FIG. 2 showing discrete carbon nanotubes on the surface and betweenplates.

EXAMPLE 3

Discrete Multiwall Carbon Nanotubes with Zirconium Phosphate Nanoplates,Zr(HP0₄)2H₂0

A dispersed solution of carbon nanotubes was prepared from 10 mg ofmulti-wall carbon nanotubes placed in 2 mL of a mixture of Zr(HP0₄)2.H₂0and tetrabutylammonium hydroxide (5 weight % Zr(HP0₄.H₂0; 1:0.8 ratio ofZr(HP0₄)2H₂0:tetrabutylammonium hydroxide). The solution wassubsequently diluted to 30 mL and then sonicated for 2 hours. Thesolution is stable for at least 24 hours. A drop of this solution isplaced on a carbon tape and dried. The secondary electron microscopepicture, FIG. 3, reveals zirconium phosphate nanoplates of approximateplate diameter of 200 nanometers interspersed with discrete carbonnanotubes.

The invention claimed is:
 1. A composition comprising: inorganic plateswith individual plate thickness of less than 10 nanometers wherein theplates are graphene nanoplates; and discrete multiwall carbon nanotubeshaving a diameter ranging from about 1 nanometer to 150 nanometers, anoxidation level of from about 1 weight % to about 15 weight %, andwherein the carbon nanotubes have an aspect ratio ranging from about 10to
 500. 2. The composition of claim 1, wherein the inorganic plates anddiscrete tubes are present at a weight ratio of about 1:100 to 100:1. 3.The composition of claim 1, wherein the inorganic plates areinterspersed with the discrete multiwall carbon nanotubes.
 4. Thecomposition of claim 1 wherein the inorganic plates are oxidized.
 5. Thecomposition of claim 1, further comprising inorganic materials selectedfrom the group consisting of: ceramics, clays, silicates, metalcomplexes and salts.
 6. The composition of claim 1 further comprising atleast one electroactive material.
 7. The composition of claim 1 furthercomprising at least one transition metal complex or active catalystspecies.
 8. The composition of claim 7, wherein the inorganic plates anddiscrete tubes are present at a weight ratio of about 1:100 to 100:1. 9.The composition of claim 1, wherein the carbon nanotubes have an aspectratio ranging from about 25 to
 500. 10. The composition of claim 1,wherein the composition is incorporated into a tire, industrial rubberpart or wind blade.
 11. The composition of claim 1, wherein thecomposition is incorporated into a battery.
 12. The composition of claim1, wherein the composition is incorporated into a capacitor.
 13. Thecomposition of claim 1, wherein the composition is incorporated into asolar cell.
 14. The composition of claim 1, wherein the composition isincorporated into a powder or liquid mixture.
 15. The composition ofclaim 1, wherein the composition is incorporated into a catalyst orcatalyst support.
 16. The composition of claim 1, wherein thecomposition is incorporated into a concrete mixture.